The present invention relates to a method and apparatus for separating the spheres from the non-spheres in particles of lamp fill material.
Modern high pressure sodium and/or mercury vapor lamps are dosed with lamp fill material which affects the operating characteristics of the lamp, such as its color and brightness. The contamination of the lamp fill material in the manufacturing process or in the dosing of the lamps with the material has a serious deleterious effect upon the lamp. The problems associated with avoiding contamination of the lamp fill material are particularly severe in the mechanized dosing operations required for the commercial production of such lamps.
The advantages of dosing lamps with particulate lamp fill material rather than a liquid are well known. These advantages include ease of handling the material and the fact that the contamination of a solid tends to be limited to the surface thereof rather than spreading throughout. It is, of course, desirable for each dose of lamp fill material to be uniform in mass so that the characteristics of the lamps may be uniform. The uniform shape of the lamp fill material is also necessary if the automatic or semi-automatic dosing machinery is to operate smoothly in performing the dosing operation.
The production of solid particles having a substantially uniform mass and composition is disclosed in the Anderson U.S. Pat. No. 4,216,178, issued Aug. 5, 1980, for "Process for Producing Sodium Amalgam Particles", and in Anderson patent application Ser. No. 207,628, filed Nov. 17, 1980, for "Method for Producing Large Diameter High Purity Sodium Amalgam Particles" issued as U.S. Pat. No. 4,419,303. By the use of such technology, controlled spheres having a normal mass distribution with a standard deviation typically five percent of the mean mass, typically three to five mg., can be produced.
However, there are things which can happen during a production run to upset the controlled formation of spheres. Control of particle size may also require adjustment during the initial start-up and final termination stages of the production process. Examples of such types of unacceptable particles are illustrated in FIGS. 4(a)-4(e) of this application.
Such unsatisfactorily shaped particles, referred to herein as "non-spheres", are mixed, of course, with the true spheres in the manufacturing process. There is a great tendency for such non-spheres to jam up a lamp dosing device by clogging a fill tube, refusing to roll, or even breaking apart, because of the very close dimensional tolerances of arc tube dosing machinery. Even though the particles are sieved to remove those particles of excessively large or small size, there generally remain non-spheres which will result in non-uniform lamp dosing and/or jamming of the dosing machinery. The period of time required by frequent un-clogging of the machinery often negates the higher production rates associated with the automatic dosing equipment.
It is thus a practical necessity to separate spheres from non-spheres prior to loading the dosing apparatus, and to do so in a dry box because of the ease of contamination. One of the prior art separation methods is the manual method of rolling particles on a flat or roughened surface. This "rough" surface method may be performed in a dry box, but requires a great many hand movements, is intolerably slow, and requires close visual examination, all of which result in severe operator strain.
Another known method of separating spheres from non-spheres is known as the "beaker" method in which the beaker is tipped on its side and the beaker wall serves as a rather shallow groove. Because the radius of curvature of the single groove is excessively large in comparison to the size of the spheres, some non-spheres such as the "twins" illustrated in FIG. 4(a), are not easily separated. Again, close visual examination and many hand movements are required which result in operator strain.
In another known method such as that disclosed in the Simmons et al U.S. Pat. No. 2,909,282, dated Oct. 20, 1959, in which the particles are placed on an inclined grooved surface with the expectation that only the spheres will roll through the grooves. In such systems, the grooved surface is a grooved endless conveyer which is moved transverse to the direction of the grooves so that the non-rolling non-spheres entering the grooves are moved transversely and dumped as the conveyor circulates. This method, while fully automatic, is not suitable for operation with lamp fill material for a number of reasons, including the relative short length of the grooves, the fact that spheres that collect behind a non-sphere are discarded with the non-sphere resulting in unacceptable yields, contamination of the particles by the conveyor material, and vibration from conveyor movement which tends to cause non-spheres to slide and, thus, pass through the grooves.
It is, accordingly, an object of the present invention to provide a novel method and apparatus for separating the spheres from the non-spheres in a large number of particles of lamp fill material.
It is a further object of the present invention to provide a novel method and apparatus suitable for use in a dry box for separating spheres from non-spheres.
It is a further object of the present invention to provide a novel method and apparatus for separating spheres from non-spheres while limiting the effects on the process of dust and/or small fragments of the particles.
It is yet a further object of the present invention to provide a novel method and apparatus for manually eliminating the non-spheres from the spheres within a dry box without risk of contamination of either the spheres or the non-spheres.
These and other objects and advantages will be readily apparent to one skilled in the art to which the invention pertains from a reading of the following detailed description when read in conjunction with the appended drawings.